1. Field of the Invention
Embodiments of the invention include a catalyst withdrawal apparatus and method for regulating catalyst inventory in one or more units. Particularly, the invention includes embodiments directed to catalyst withdrawal apparatus and method for regulating catalyst inventory in one or more fluid catalytic cracking units.
2. Description of the Related Art
A fluid catalytic cracking system generally includes a fluid catalytic cracking unit (FCCU) coupled to a catalyst injection system that maintains a continuous or semi continuous addition of fresh catalyst to the inventory circulating between a regenerator and a reactor.
During the catalytic process, there is a dynamic balance of the total catalyst within the FCC unit. For example, catalyst is periodically added utilizing the catalyst injection system and some catalyst is lost in various ways such as through the distillation system, through the effluent exiting the regenerator, etc.
If the amount of catalyst within the FCC unit diminishes over time, the performance and desired output of the FCC unit will diminish, and the FCC unit will become inoperable. Conversely, if the catalyst inventory in the FCC unit increases over time or becomes deactivated, the catalyst bed level within the regenerator reaches an upper operating limit and the deactivated or excess catalyst is withdrawal to prevent unacceptably high catalyst emissions into the flue gas stream, or other process upsets.
Thus, there is a need for a catalyst withdrawal apparatus suitable for use with a fluid catalytic cracking catalyst unit.